A known device for accessing interactive audiovisual programs is the Compact Disc Interactive (CDi) player. A large amount of multimedia applications have been developed for this device. A CDi disc comprises an audiovisual program and application software. The application software allows a user to access the program material in an interactive manner. For example, after displaying a particular program item, the player stops and the user is given the opportunity to indicate whether he wants the program item to be repeated or to proceed to a different program item. User commands are given by moving a cursor in a graphic menu. Upon activating the cursor, the application software determines from which location on disc the recorded program is to be continued.
The audiovisual program, application software and graphic images are collectively referred to as "real-time" file. The real-time file is stored on a plurality of sectors of the CDi disc. The CDi system ensures that related assets within a real-time file are kept together and that all assets needed for a given application are delivered in real-time with proper synchronization of video, audio, and graphics overlays augmenting the audiovisual program.
A CDi player is a stand-alone system. The real-time file is stored on tracks of the CDi disc. The storage format is specified in "CDi Full Functional Specification", Philips Consumer Electronics B.V., March 1993, usually referred to as the Green Book. As far as relevant to the invention, the storage format will now be summarized. The CDi disc has a lead-in track, up to 99 information tracks, and a lead-out track. Information tracks can carry either CDi data or digital audio (DA). They are referred to as CDi tracks and DA tracks, respectively. With each track, eight subcode channels are associated, usually denoted PQRSTUVW subcode channels. The subcode channels contain control and display information. CDi tracks are divided into sectors of 2352 bytes. With each sector, 98 bytes of subcode data are associated. DA tracks are divided into audio blocks of 2352 bytes. With each audio block, 98 bytes of subcode data are associated. The format of DA tracks complies with the well-known compact disc digital audio specification as defined in "CD-DA System description", Sony Corp. and N.V. Philips, November 1991, also referred to as the Red Book. Further, the Q subcode channel associated with the lead-in track contains the table of contents (TOC) of the disc.